Method and apparatus for steering strip material through rolling mills

ABSTRACT

DESCRIBED ARE A METHOD AND APPARATUS FOR STEERING STRIP MATERIAL THROUGH A ROLLING MILL, PARTICULARLY WHEN THE MILL IS BEING THREADED, IN A MANNER TO PREVENT THE STRIP FROM TURNING OFF THE CENTER LINE OF THE MILL DUE TO CAMBER (I.E., ONE EDGE OF THE STRIP BEING THICKER THAN THE OTHER). THIS IS ACCOMPLISHED BY ADJUSTING THE SPACING BETWEEN THE ROLLS AT THEIR OPPOSITE ENDS SO AS TO EQUALIZE THE ROLL FORCES ON OPPOSITE EDGES OF THE STRIP AS IT IS THREADED THROUGH THE ROLLS. AFTER THE STRIP IS, THREADED THROUGH THE ROLLS AND TENSION APPLIED THERETO, EITHER BY A SUCCEEDING ROLL STAND OR BY A COILER, THE ROLLS CAN BE ADJUSTED TO MAINTAIN THE SPACING BETWEN THEIR OPPOSITE EDGE THE SAME OR NEARLY THE SAME. THE INVENTION ALSO ENCOMPASSES STRIP STEERING FOR THE PURPOSES AS WELL AS STRIP STEERING COMBINATION WITH STRIP SHAPING AND GAGE CONTROL.

United States Patent 4 Inventor Joseph A. McCarthy Williamsville, N.Y.

[2]] Appl. No. 782,599

221 Filed nee lo, 1968 [45] Patented June 28, 1971 [73 Assignee to Westinghouse Electric Corporation. Pittsburgh. Pa.

[54] METHOD AND APPARATUS FOR STEERING STRIP MATERIAL THROUGH ROLLING MILLS 12 Claims, 3 Drawing Figs.

52 us. Cl 72/8 [51] 1nt.Cl B2lb37/00 [50] Field of Search 72/8, 9, 10, ll, 12, 16,20,27

[56] References Cited UNITED STATES PATENTS 3,204,441 9/1965 Lyle 72/231 3,213,655 l0/1965 Reid 72/11 3,245,241 4/1966 Roberts 72/12X 3,318,124 5/l967 Plaisted 72/8 Primary Examiner- Milton S. Mehr Attorneys-F. H. Henson and R. G. Brodahl ABSTRACT: Described are a method and apparatus for steering strip material through a rolling mill, particularly when the mill is being threaded, in a manner to prevent the strip from turning off the center line of the mill due to camber (i.e., one edge of the strip being thicker than the other). This is accomplished by adjusting the spacing between the rolls at their opposite ends so as to equalize the roll forces on opposite edges of the strip as it is threaded through the rolls. After the strip is threaded through the rolls and tension applied thereto, either by a succeeding roll stand or by a coiler, the rolls can be adjusted to maintain the spacing between their opposite edges the same or nearly the same. The invention also encompasses strip steering for other purposes as well as strip steering in combination with strip shaping and gage control.

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WITNESSESI INVENTOR Joseph A. McCorth'y METHOD AND APPARATUS FOR STEERING STRIP MATERIAL THROUGH ROLLING MILLS BACKGROUND OF THE INVENTION When a length of metal strip material is threaded through a rolling mill, there is sometimes a tendency for the strip to curve or turn off the mill centerline due to its being thicker at one edge than the other. Normally, the mill stand rolls are leveled, meaning that the spacing between them at their opposite ends is substantially the same. When cambered strip, thicker at one edge than the other, enters such leveled rolls, the rolls attempt to produce a uniform thickness across the width of the strip. This produces a greater roll force at one end of the rolls than at the other end; and since the rolls attempt to take a greater reduction at the thicker edge, the resulting length of the material leaving one end of the rolls tends to be greater than at the other end. This causes a bowed condition in the strip, causing it to turn off the centerline of the mill and making it difficult to thread the strip through a succeeding roll stand of the mill or into a coiler. Considerable productive time is lost due to this tendency of the strip to turn off center during threading operations; and since the productivity of any metal reducing roll mill facility is directly related to the ability of the the strip to turn off center is, of course, highly undesirable.

SUMMARY OF THE INVENTION As one object, the present invention provides new and improved method and means for steering metal strip material through a rolling mill whereby the strip can be caused to pass along a straight line path parallel to the mill center line.

More specifically, an object of the invention is to provide an improved steering system and method for strip material passing through a rolling mill wherein the roll forces at opposite ends of the rolls are measured, and if the roll forces are not the same, indicating a cambered condition of the strip material passing through the mill, the roll spacing at a selected edge of the strip is changed whereby the roll forces are the same.

Still another object of the invention is to provide a combined strip steering and gage control system for a rolling mill wherein roll force measurements are taken at the opposite ends of the rolling mill rolls and utilized in a combined strip steering, strip shaping and strip gage control system.

A still further object of the invention is to provide a new and improved method for steering strip material through a rolling mill, including strip shaping and strip gage control functions.

In accordance with the invention, means areprovided for producing a first electrical signal which varies as a function of the roll force at one end of rolling mill rolls through which strip material passes, and further means are provided for producing a second electrical signal which varies as a function of the roll force at the other end of the aforesaid rolls. The first and second electrical signals are compared to derive a differential electrical signal and this differential signal is used to vary the spacing between one end of the rolls until said roll forces are substantially equal and said differential signal is zero, or some empirically derived offset value near zero.

Further, in accordance with the invention, control of roll forces at opposite ends of the rolls can be utilized to steer the strip through the mill, either under threading conditions or otherwise, to shape the rolls, and to control gage. This is done preferably by means of a computer, responsive to various'mill parameters, which regulates the roll forces at opposite ends of the'rolls. A

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

' FIG.1 is a schematic illustration of the effect of camber in strip material on rolling mill rolls;

. FIG. 2 is a schematic diagram of one embodiment of the present invention particularly adapted for use in rolling mill threading operations; and

FIG. 3 illustrates a computer-controlled combined strip steering, strip shaping and strip gage control system.

With reference now to the drawings, and particularly to FIG. I, the strip material being rolled between rolls I0 and I2 is identified by the reference numeral I4, the thickness of the strip being greatly exaggerated for purposes of explanation. It will be noted that the right side of thestrip is thicker than the left side. Normally, the screwdowns on the opposite ends of the rolls are adjusted such that the spacing between the rolls at their opposite ends is substantially the same. It can be readily appreciated, however, that when a cambered strip, thicker at one side than the other, is threaded through rolls [0 and 12 which are'spaced apart in equal amounts at their opposite ends, the roll force at the right side will be much greater than at the left. Furthermore, the strip, in passing through the parallel rolls I0 and I2, will tend to curve or bow off to the left of the centerline of the mill, making it difficult to thread it through a succeeding roll stand or into a coiler. v

Apparatus for preventing the strip from turning off the centerline of the mill during threading is shown in FIG. 2. Two rolling mill stands are shown and identified as SI and S2. Each stand includes a pair of work rolls I6 and 18 and associated backup rolls 20 and 22. At the opposite sides of the stand 81, for example, are screwdown mechanisms schematically illustrated at 24 and 26. These screwdown mechanisms, however, can be replaced with equivalent wedge systems or mechanical linkages designed to regulate the spacing between the rolls, all within the skill of the art. In accordance with well known practice, the screwdown mechanisms 24 and 26, driven by means of motors 28 and 30, control the screwdown force or pressure on journals at the opposite ends of the roll 20. Alternatively, the mechanisms 24 and 26 can be driven by means of equivalent electrical or hydraulic actuators. Screwdown motors 28 and 30, in turn, are controlled by screwdown motor control circuits 32 and 34, respectively. The screwdown motors 28 and 30 are normally controlled by means of a gage control circuit 36 which maintains the spacing between the work rolls [6 and 18 at their opposite ends substantially the same.

Beneath the opposite ends of lower work roll 22 are left and right load cells 37 and 38, respectively. These load cells produce signals on leads 40 and 42 proportional to the roll forces imparted by the respective screwdown mechanisms 24 and 26. The rolls for stands SI and S2 are driven by drive motors, schematically illustrated as M1 and M2.

The electrical signals proportional to the roll forces at the left'and right ends of the rolls are applied via leads 40 and 42 to a differential amplifier 44 which will produce identical outputs on leads 46 and 48 comprising angelectrical signal proportion to the difference between the magnitude of the signals on leads 40 and 42. The roll force signals on leads 40 and 42 are also applied to two comparators 50 and 52. Comparator 50 will produce an output signal on lead 54 when the rollforce signal on lead 40 is greater than that on lead 42. Similarly, the comparator 52 will produce an output signal on lead 56 when the right roll force signal on lead 42 is greater than that on lead 40. The signals on leads 46 and 54 are applied to a gate 58, the signal on lead 54 acting to enable the gate. Thus, assuming that the left roll force is greater than the right roll force, a signal will appear on lead 54 to enable gate 58 which then passes the differential signal from amplifier 44 to lead 60. Assuming that thegate 62 is enabled, the signal on lead 60 will be applied to the screwdown control circuit '32 to activate motor 28 and raise the screw mechanism 24. As the left screw 24 is raised, the roll force signal on lead progressively decreases until the output of the differential amplifier 44 is gate 70 is enabled, this signal will be applied to the right screwdown control circuit 34 which activates screwdown motor 30 to raise the right screw mechanism 26 until the roll forces are again equal.

A current sensor 74 is provided for the armature of motor M1 and, similarly, a current sensor 76 is provided for the armature of motor M2. When the strip initially enters the roll bite between work rolls l6 and 18 of stand S], the current through the motor armature will increase. This increase in motor armature current through motor Ml generates a signal on lead 78 which enables the gates 62 and 70. At the same time, the signal on lead 78 disables gate 80 through which signals from the gage control circuit 36 are applied to the screwdown control circuits 32 and 34. Thus, once the strip enters the roll pass of stand S1, conventional gage control is no longer effective, and the screwdowns are controlled by the output of differential amplifier 44 which causes the roll forces at opposite ends of stand 51 to be substantially equal in the manner described above.

As the strip 14 progresses through stand S1, its forward end will eventually reach stand S2; and as it reaches the stand S2 and enters the roll bite thereof, the current through the armature of motor M2 will increase, thereby generating a signal on lead 82 which now disables gates 62 and 70 while enabling gate 80 relative to the operation of stand S1. At this point, tension is applied to the strip which has now been threaded through both of the stands S1 and 82. Once tension is applied, the strip is more or less forced to travel along a straight line path between the two stands; and when gate 80 is enabled, gage control circuit 36 causes the screwdowns 24 and 26 to again equalize the spacing between the work rolls 16 and 18 at their opposite ends, notwithstanding any chamber which might be present in the strip.

Various types of gage control systems may be utilized such as a more or less simple feedback system wherein the gage at the output of a stand is measured by a suitable thickness gage, such as X-ray gage 84. However, a roll force gage control system may also be utilized in accordance with the equation:

where h =delivery gage,

S screwdown setting,

F=roll force, and

M slope of the mill spring line (a constant). If a level roll condition is provided for a given stand, and the input strip has the same thickness at each edge, then the following relationship should prevail:

where the subscripts (L) and (R) signify the left and right sides of the rolls, respectively. It will happen, however, that the roll forces at the opposite sides of the mill arenot necessarily equal. Accordingly, the signals on leads 40 and 42 are applied to a signal averaging circuit 86 which produces an output signal proportional to the average roll forces on opposite sides of the mill. This signal is then applied to the gage control circuit 36 where the foregoing equation:

is solved to derive a signal proportional is S in relation to a desired delivery gage.

With reference now to FIG. 3, a computer-controlled circuit is shown which provides strip steering during threading, gage control, load distribution of stand motor, and scheduled successive stand screwdown settings. The rolling millincludes five stands, only stands S1, S2 and S being shown for purposes of illustration. At the end of the mill is a conventional coiler 81 driven by motor 83 and controlled by motor control circuit 85. Each stand is provided with a screwdown mechanism SCl, SC2 and SC5, which incorporates means for controlling the roll forces on opposite ends of the rolls for each stand. Left and right roll forces are sensed by load cells LIL, LlR, L2L, L2R, and so on. In order to determine the thickness at the opposite edges of the strip, two input X-ray gages 88 and 90 are employed, the thickness of the material sensed by these gages being fed to a control computer 92 along with screw settings sensed by screwdowns SCI, SC2 and so on. The roll forces are sensed by lead cells LlL, LlR, L2L, and so on; and final exit gage is sensed by X-ray gage 94. Each of the stands is provided with a drive motor M1 through M5, and the tension in the strip between the stands is sensed by tensiorneters Tl through T4 which produce electrical signals, proportional to tension, which are fed to computer 92. The computer 92 is provided with a predetermined stored program in its memory as shown.

With an arrangement such as that shown in FIG. 3, camber in the entering strip can be sensed by the X-ray gages 88 and 90 by virtue of a variation in the thickness of the strip at its opposite edges. This information, when fed to the master control computer 92, can be used to adjust the screwdown SCl, for example, in order to adjust the spacing between the rolls as desired at their respective ends even before the strip enters the roll bite to maintain the left and right roll forces substantially the same until threading through the first stand and into the second stand is completed as sensed, for example, by a surge in armature current of the motor M2.

When the strip enters the second stand S2, the computer 92 corrects the strip shape out of the first stand relative to input strip shape errors as sensed by the two X-ray gages 88 and 90 through suitable adjustment of either the right or the left screwdown for stand S1 as required. At this point, of course, strip steering is no longer a problem relative to the first stand since the strip is held in position by the second stand. If desired, reduced shape corrections can be fed forward into the second stand and even the third and succeeding stands to correct input strip shape errors within the limits of desired steering of the strip.

In the description given in connection with the embodiment of FIG. 2, and in the embodiment of FIG. 3, a reduction in gage can be taken during threading while still maintaining the roll forces at opposite ends of the rolls the same, in accordance with the equation:

where the subscripts (R) and (L) again signify the left and right sides of the rolls, respectively. This equation can be solved by the computer to derive S and 8,, for a desired average output gage, notwithstanding the fact that the thickness of the strip will be greater at one edge than the other and with the opposite roll forces being equal to maintain desired strip steering characteristics.

Whenthe strip enters the windup reel, and the reel motor load therefore indicates that this has happened, and mass flow gage control principles can be used with interstand tensions controlled to determine the delivery thickness from each of the stands, and final gage can be corrected, if necessary, from a reading obtained by the final output X-ray gage 94. As will be understood, the reading from gage 94 will override computed, desired output gage as determines from mass flow or roll force gage control techniques.

Drive motor speeds are controlled by readings from the tensiometers. The computer 92 can be programmed in advance with known roll bending characteristics as a function of F compared with F This can be utilized for roll bending and shape control purposes.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

I claim:

1. In the method of threading metal strip material through a rolling mill wherein the strip material is reduced in passing between opposed rolls, the steps of rotating said rolls and feeding the end of said strip material into the roll bite between said rolls, and adjusting the spacing between said rolls at the opposite ends thereof as strip material is threaded through said rolling mill until the roll forces at said opposite ends are substantially equal and the strip material leaves the rolls along a substantially straight-line path.

2. In the method of threading metal strip material through a rolling mill wherein the strip material is reduced in passing between opposed rolls, the steps of rotating said rolls and feeding the end of said strip material into the roll bite between said rolls, adjusting the spacing between said rolls at the opposite ends thereof until the roll forces at said opposite ends are substantially equal and the strip material leaves the rolls along a substantially straight-line path, applying tension to said strip material after it has passed through the rolls, and again adjusting said rolls until the spacings between their opposite ends are substantially equal.

3. The method of claim 2, including the step of varying the roll forces on said rolls after tension is applied to said strip material to maintain the gage of said strip material substantially constant across its width as it progresses through said rolls.

4. The method of claim 2, including the step of measuring the gage of strip material at the opposite edges thereof before the strip material enters the roll bite between said rolls, and adjusting the spacing between the opposite ends of said rolls as a function of the measured gage of said strip material at its opposite edges.

5. The method ofclaim 1, wherein said rolling mill includes a plurality of opposed rolls arranged in tandem and through which said strip material passes, and including the step of maintaining the roll forces at the opposite ends of each set of rolls substantially equal until the strip material enters the bite of the next succeeding pair of tandem rolls.

6. The method of claim 2, including the step of reducing the thickness of said strip material while maintaining said roll forces at the respective opposite ends of said rolls substantially equal.

7. In a rolling mill of the type in which strip material is reduced in passing between opposed rolls, the combination of means for producing a first electrical signal which varies as a function of the roll force at one end of said rolls, means for producing a second electrical signal which varies as a function of the roll force at the other end of said rolls, means for comparing said first and second electrical signals to produce a differential signal, and rolling mill screwdown apparatus responsive to said differential signal and operative only before ten sion is applied to the strip material passing between said rolls for varying the spacing between at least one end of the rolls until said roll forces are substantially equal and said differential signal is substantially zero.

8. The combination of claim 7, wherein the means for producing said first and second electrical signals comprises load cells disposed at opposite ends of said rolls.

9. The combination of claim 7, including signal gate means for applying said differential signal to said screwdown apparatus, means for generating an electrical signal when tension is applied to the end of strip material passing through said rolls, and means for applying said last-named electrical signal to said signal gate means to disable the same.

10. The combination of claim 9, including means for controlling the gage of strip material passing through said rolls, and second signal gate means responsive to said last-named electrical signal for connecting said gage controlling means to said screwdown apparatus when tension is applied to the end of said strip material passing through the rolls.

1]. The combination of claim 7, wherein the means for comparing said first and second electrical signals to produce a differential signal comprises a differential amplifier, a pair of gating devices, means for applying the output of said differential amplifier to both of said gating devices, means for enabling one of said gating devices when sald first electrical signal is greater in magnitude than said second electrical signal, means for enabling the other of said gating devices when said second electrical signal is greater than said first electrical signal, a first screwdown mechanism for one side of said rolls, means connecting the output of said first gating device to said first screwdown mechanism, a second screwdown mechanism for the other side of said rolls, and means connecting the output of said second gating device to said second screwdown mechanism.

12. The combination of claim 7, including means for measuring the gage of said strip material at its opposite edges before it passes between said rolls, and computer means operatively connected to said gage measuring means for adjusting the spacing between the respective ends of the rolls. 

